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ESD Protection design of PCB

Release time: 25/10/2018

Static electricity is everywhere in our life, and on the PCB is no exception. But static electricity will have a direct failure of the components of the damage, so we in the PCB design will have a lot of protection design. PCB on the Integrated Circuit (IC) subjected to electrostatic discharge, the purpose of equipment safety grounding is to prevent the case when charged (leakage or high voltage contact) General Electric shock, which is also connected to 0 protection problems. This is also to prevent electrostatic discharge (including lightning) damage equipment.
In the design of PCB board, it can realize the anti-ESD design of PCB through layering, proper layout and wiring and installation. In the design process, the majority of design modifications can be limited to increase or decrease the components, by adjusting the PCB layout and cabling, can be a good protection against ESD. From the human body, the environment and even electric PCB copy board equipment inside the static PCB copy plate power for precision semiconductor chips will cause a variety of damage, such as penetrating the components of the internal thin insulation layer, damage to the MOSFET and CMOS components of the gate; CMOS PCB copy of the trigger lock, short-circuit reverse partial PN junction , short circuit is PCB copy plate to offset the PN junction, PCB copy board to melt the active part of the PCB Copy Board section of the welding line or aluminum wire. In order to eliminate the interference and destruction of electrostatic discharge on electronic equipment, a variety of technical measures are needed to prevent it. In the PCB design, can be layered, the appropriate layout of PCB copy board PCB copy board wiring and installation to achieve the anti-ESD design of the PCB. In the design process, the majority of design modifications can be limited to adding or subtracting components through forecasts. Through the adjustment of PCB layout and cabling, can be very good to prevent PCB copy board ESD.

anti-ESD design of PCB

Here are some common precautions. Using multilayer PCBs as much as possible, the ground plane and the power plane, and the tightly spaced signal line-ground spacing can reduce common-mode impedance and inductive coupling to 1/10 to 1/100 of the duplex PCB, relative to the duplex PCB. Try to keep each signal layer close to a power layer or ground layer. For high-density PCBs with components on both the top and bottom surfaces, with very short connectors, and many fill floors, consider using inner lines. For double-sided PCBs, a tightly interwoven power supply and ground grid are used. The power cord is close to the ground and is connected as much as possible between the vertical and horizontal lines or the fill area. One side of the grid PCB copy board size is less than or equal to 60mm, if possible, the grid size should be less than 13mm. Make sure every circuit PCB copy board is as compact as possible. Put all connectors on one side as much as possible. If possible, introduce the power PCB copy board line from the center of the card and away from areas that are prone to direct ESD impact.
On all PCB layers below the connector that leads to the outside of the chassis (easy for PCB copy board to be hit directly by ESD), place a wide chassis or polygon fill, and connect them with vias every approximately 13mm away. On the edge of the card to put PCB copy board mounting hole around the installation hole with the PCB copy board the top layer of the flux and the bottom pad connected to the chassis floor. When assembling the PCB, do not apply any solder on the top or bottom PCB copy board pads. Use a screw with an inline PCB copy plate washer to achieve a close contact between the PCB and metal chassis PCB copy board/shielding layer or ground bracket. The same "containment area" should be set between the chassis ground and the circuit ground in each layer, and if possible, keep the distance of 0.64mm. At the top of the card and the bottom layer near the PCB copy board mounting hole location, every 100mm along the chassis ground line will be chassis and circuit with 1.27mm wide lines connected together. Adjacent to these connection points, place a pad or mounting hole for mounting between the chassis ground and the circuit PCB copy board. These ground connections can be cut off with a blade to maintain an open circuit, or by jumping with a high-frequency capacitor of magnetic beads. If the circuit board is not placed in a metal case or PCB shield device, the top layer of the circuit board and the ground floor of the chassis can not be coated with solder, so that they may be used as ESD arc discharge pole.
To the following PCB copy plate in the way around the circuit set a circular ground: In addition to the edge of the PCB copy board and the chassis ground, around the entire periphery of the ring-like path. Ensure that the annular width of all layers is greater than 2.5mm. Every 13mm used holes will be connected in a ring. The annular ground is connected to the common ground of the multilayer PCB copy board circuit. For the double-sided PCB copy board installed in the metal case or shielding device, the annular ground should be connected with the circuit in a common way. unshielded double-sided circuit should be looped to the chassis, the ring on the ground can not be applied to the solder, so that the ring may act as an ESD discharge rod, in the ring (all layers) on a position at least a 0.5mm wide gap, so that the PCB copy board to avoid forming a large loop. The distance of the signal wiring from the annular ground cannot be less than 0.5mm.
PCB Welding Electrostatic Protection method: circuit board welding equipment must be grounded well, the workshop to maintain constant temperature, humidity environment. Should be equipped with anti-static material box, turnover box, PCB frame, anti-static wrist strap and other facilities. The static safety zone is 23±3℃ at room temperature and the relative humidity is 45-70%rh. It is forbidden to operate the electrostatic sensitive element in less than 30% of the environment. Non-production items such as tableware, tea sets, handbags, woolen fabrics, newspapers, rubber gloves, etc. are prohibited on the work Bench of the electrostatic safety zone. The worker enters the work area to be discharged. The operator must wear work clothes and no textile gloves on hand. Wear an antistatic wrist strap during operation and measure the wrist strap every day for effectiveness. Hair should not be scattered and must be jammed with a card. When mounting electrostatic sensitive devices, you should take one piece from the box, tube, and plate, and do not pile it on the table, nor fall off to the ground. Warehouse relative Humidity: 30-40%rh. Board processing process may not be arbitrarily stacked, all shelves.